There is an ongoing need for embedding auxiliary digital data within primary digital data (sometimes referred to as content or user content). The auxiliary data may be used, for example, for identification of ownership, or origin, or usage control information. A digital watermark is auxiliary data, embedded in primary digital data, created by modifying the primary digital data. Since the original data is modified, digital watermarks are typically confined to human perceptible data such as audio, image, and video, and the data is typically modified in such a way that the digital watermark is “transparent” (not perceptible).
A digital watermark can serve as an indicator of usage control if present, but it is theoretically possible to remove a digital watermark from primary data that originally included a watermark, resulting in useable unprotected primary data. In addition, some common transformations of entertainment data, such as compression, scaling and clipping may alter or destroy a digital watermark. Alternatively, a system may require the presence of a valid watermark, and the system may refuse to read the primary data, or refuse to provide an output, if a valid watermark is not present. It is theoretically possible to add or modify a watermark to enable unauthorized use or copying.
There is a need for persistent digital watermarking that can deter intentional and unintentional destruction and removal, and that can deter casual addition or modification.